1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display used as a display of an information apparatus, a liquid crystal display having the same, and a method of manufacturing the same.
2. Description of the Related Art
As liquid crystal displays having finer pixels and an improved aperture ratio, attentions are being paid to liquid crystal displays having a CF-on-TFT (color filter on thin film transistor array) structure in which color filter resin layers are formed on a thin film transistor (TFT) substrate.
FIG. 17 shows a configuration of a liquid crystal display in the related art having the CF-on-TFT structure. As shown in FIG. 17, a plurality of gate bus lines 110 extending in the horizontal direction in the figure are formed in parallel with each other on a TFT substrate 102 (only one line is shown in FIG. 17). A plurality of drain bus lines 112 extending in the vertical direction in the figure are formed in parallel with each other such that they intersect the gate bus lines 110 with an insulation film which is not shown interposed therebetween. TFTs 114 are formed in the vicinity of the positions where the bus lines 110 and 112 intersect. Drain electrodes 116 of the TFTs 114 are electrically connected to the drain bus lines 112. Source electrodes 118 of the TFTs 114 are formed opposite to the drain electrodes 116.
A plurality of storage capacitor bus lines 120 are formed on the TFT substrate 102 in parallel with the gate bus lines 110 (only one line is shown in FIG. 17). Storage capacitor electrodes 122 are formed on the storage capacitor gate bus lines 120 with an insulation film which is not shown interposed therebetween. Storage capacitances are formed by the storage capacitor bus lines 120 and the storage capacitor electrodes 122.
A CF resin layer in any of red (R), green (G), and blue (B) is formed in each of pixel regions of the TFT substrate 102. Leveling resin films (overcoat layers) and pixel electrodes 132 are formed on the CF resin layers. The pixel electrodes 132 are electrically connected to the source electrodes 118 through contact holes 130 and are connected to the storage capacitor electrodes 122 through contact holes 131. That is, the source electrodes 118 are electrically connected to the storage capacitor electrodes 122 through the pixel electrodes 132.
A method of manufacturing the TFT substrate of a liquid crystal display according to the related art having the CF-on-TFT structure will now be described with reference to FIGS. 18 and 19. FIG. 18 is a flow chart showing steps for manufacturing the TFT substrate having the CF-on-TFT structure according to the related art. First, a metal layer is formed and patterned throughout a top surface of a glass substrate to form the gate bus lines (gate electrodes) 110 and the storage capacitor bus lines 120 (step S21). Next, an insulation film (gate insulation film) is formed on the entire surface (step S22). Next, a metal layer is formed and patterned on the entire surface of the gate insulation film to form the drain electrodes 116, the source electrodes 118, the drain bus lines 112, and the storage capacitor electrodes 122 (step S23).
FIG. 19 shows a configuration of the TFT substrate 102 at the point in time when the process at step S23 has been completed. As shown in FIG. 19, since the pixel electrodes 132 have not been formed yet at the point in time when the process at step S23 has been completed, the source electrodes 118 and the storage capacitor electrodes 122 are not electrically connected.
Referring to FIG. 18 again, a protective film is formed on the entire surface of the drain electrodes 116, source electrodes 118, drain bus lines 112, and storage capacitor bus lines 122 (step S24). Next, any of the CF resin layers R, G, and B is formed in each of the pixel regions on the protective film (step S25). Next, the overcoat layer is formed on the CF resin layers (step S26). Openings are then formed in the overcoat layer, the CF resin layers, and the protective film above the source electrodes 118 and the storage capacitor electrodes 122 to form the contact holes 130 and 131, respectively (step S27). Next, a pixel electrode 132 constituted of an ITO (indium tin oxide) is formed in each pixel region (step S28). At this time, the pixel electrodes 132 are electrically connected to the source electrodes 118 through the contact holes 130 and are electrically connected to the storage capacitor electrodes 122 through the contact holes 131. An array inspection (step S29) is then conducted.
At the array inspection, for example, a predetermined voltage is applied to the drain bus lines 112 to turn on the TFTs 114 and to thereby charge the storage capacitance at each pixel with a predetermined charge, and the charge stored at each pixel is measured to detect a defect by checking whether the charge is in the excess of a threshold or not. When a defect is detected at the array inspection, the process proceeds to step S30 where predetermined repair is performed using a laser on the defect, and the process then returns to step S29. When no defect is detected at the array inspection, the process proceeds to step S31 to conduct a visual inspection.
The array inspection is conducted after it becomes possible to charge the storage capacitance at each pixel with a charge. In the configuration of the TFT substrate 102 according to the related art, the source electrodes 118 and the storage capacitor electrodes 122 are electrically connected through the pixel electrodes 132 formed on the CF resin layers. Therefore, the array inspection is conducted on the TFT substrate 102 having the CF-on-TFT structure after the CF resin layers R, G, and B and the pixel electrodes 132 are formed.
The CF resin layers R, G, and B provide a light-blocking function when at least two such layers are formed in an overlapping relationship. Therefore, at least two of the CF resin layers, R, G, and B are formed on the TFTs 114 and a frame area around a display area.
FIG. 20 shows a configuration of a frame area of the TFT substrate 102 according to the CF-on-TFT-structure of related art. As shown in FIG. 20, a frame area 152 is provided around a display area 150 of the TFT substrate 102. At least two of the CF resin layers R, G, and B are stacked except in some regions to be described later.
FIG. 21 is an enlarged view of the region enclosed by a circle a shown in FIG. 20. Repair wirings 154, 155, and 158 for repairing breakage of the drain bus lines 112 are formed such that they avoid the display area 150 in the frame area 152 as shown FIG. 21. The repair wirings 154 intersect a plurality of drain bus lines 112 with an insulation film interposed therebetween at respective connecting portions 156. The repair wirings 155 intersect a plurality of drain bus lines 112 with the insulation film interposed therebetween at respective connecting portions 157. One end of the repair wirings 158 is formed on one end of the repair wirings 154 with the insulation film interposed therebetween at a connecting portion 160.
When a drain bus line 112 that has been broken is repaired, the connecting portion 156 of the drain bus line 112 is irradiated with a laser beam to electrically connect the drain bus line 112 and the repair wiring 154. Further, the connecting portion 160 is irradiated with a laser beam to electrically connect the repair wirings 154 and 158. The drain bus line 112 is repaired by bypassing a tone voltage using the repair wirings 154 and 158.
As shown in FIG. 21, only one of the CF resin layers R, G, and B is formed instead of two in the regions in the vicinity of the connecting portions 156, 157, and 160 that are irradiated by a laser beam. Since those regions are therefore not shaded, the connecting portions 156, 157, and 160 can be visually checked, which makes it easy to irradiate the connecting portions 156, 157, and 160 with a laser beam.
However, when such a configuration is employed, since the neighborhood of the connecting portions 156, 157, and 160 of the frame area 152 is not shaded, light leaks in the vicinity of the connecting portions 156, 157, and 160. Since the connecting portions 156, 157, and 160 are provided in the vicinity of the display area 150, the leakage of light from those portions results in the problem of a reduction of display quality.
At least two of the CF resin layers R, G, and B are stacked on the TFTs 114, the gate bus lines 110, and the drain bus lines 112 for the purpose of shading. This results in a problem in that it is difficult to detect the exact position of a defect at a visual inspection using a microscope even when the defect is electrically detected at an array inspection.
Although not shown, outside the display area 150 of the TFT substrate 102, there is formed an inner-short-ring for preventing electrostatic discharge damage that remains when the product is completed. Outside the inner-short-ring, there is formed an outer short ring for preventing electrostatic discharge damage that is cut off and discarded at a subsequent step. The two short-rings are connected through the bus lines 110, 112, and 116 and TFTs for preventing electrostatic discharge damage. This prevents any shift of a threshold of TFTs and inter-layer shorting that otherwise occurs when the bus lines 110, 112 and 116 are charged with static electricity.
A gate electrode and a drain electrode of a TFT for preventing electrostatic discharge damage are electrically connected to the same bus line 110, 112, or 116 or the same short-ring such that it is turned on when the respective bus line 110, 112, or 116 is charged with static electricity having a high potential. In the related art, the gate electrode and drain electrode of a TFT for preventing electrostatic discharge damage are electrically connected through a contact hole provided by forming an opening in a protective film and an insulation film on a gate metal layer electrically connected to the gate electrode, a contact hole provided by forming an opening in a protective film on a drain metal layer electrically connected to the drain electrode, and an ITO layer formed between those contact holes.
However, since one or two or all of the CF resin layers R, G, and B are formed under the ITO layer, an opening must be formed through the CF layers, R, G and B to form those contact holes. Therefore, the regions where the contact holes are formed are not shaded, which can cause light to leak from the frame area 152. This results in a problem that display quality is reduced by the leakage of light.